"The end" ran through his mind, to the exclusion of all speakable thoughts.
The things that are not to be said in English are not worth thinking—if they are speakable at all; and some things are not.
The sisters' lips were sealed; the only speakable person on the premises was Woolly.
Old English specan, variant of sprecan "to speak" (class V strong verb; past tense spræc, past participle sprecen), from Proto-Germanic *sprekanan (cf. Old Saxon sprecan, Old Frisian spreka, Middle Dutch spreken, Old High German sprehhan, German sprechen "to speak," Old Norse spraki "rumor, report"), cognate with Latin spargere "to strew" (speech as a "scattering" of words; see sparse).
The -r- began to drop out in Late West Saxon and was gone by mid-12c., perhaps from influence of Danish spage "crackle," in a slang sense of "speak" (cf. crack in slang senses having to do with speech, e.g. wisecrack, cracker, all it's cracked up to be). Rare variant forms without -r- also are found in Middle Dutch (speken) and Old High German (spehhan).
Not the primary word for "to speak" in Old English (the "Beowulf" author prefers maþelian, from mæþel "assembly, council," from root of metan "to meet;" cf. Greek agoreuo "to speak," originally "speak in the assembly," from agora "assembly").